SQL · Theory

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Theory

272/439

Comments

-- this is a line comment (space after --). # also works in MySQL. /* block comment */ can span lines.

Don’t put secrets in comments in dumps. Nested /* */ can surprise you.

Trap — --comment without a space after -- in some clients.

On the example next to this theory: Comments: create two demo rows, then SELECT qty >= 2 ordered. Say which labels come back.

Exam tip

-- comment and /* block */

Comments — sample query

-- Comments
CREATE TABLE demo (
  id INTEGER PRIMARY KEY,
  label TEXT NOT NULL,
  qty INTEGER DEFAULT 0
);
INSERT INTO demo (id, label, qty) VALUES
  (1, 'alpha', 2),
  (2, 'beta', 5);
SELECT label, qty FROM demo WHERE qty >= 2 ORDER BY qty DESC;

Comments: create two demo rows, then SELECT qty >= 2 ordered. Say which labels come back.

Short notes

Def-- and /* */ comments. # in MySQL.
RuleSpace after -- .
TrapPassword in a commented dump line.

SQL · Theory

Comments

← All stacks

Theory

272/439

Comments

-- this is a line comment (space after --). # also works in MySQL. /* block comment */ can span lines.

Don’t put secrets in comments in dumps. Nested /* */ can surprise you.

Trap — --comment without a space after -- in some clients.

On the example next to this theory: Comments: create two demo rows, then SELECT qty >= 2 ordered. Say which labels come back.

Exam tip

-- comment and /* block */

Comments — sample query

-- Comments
CREATE TABLE demo (
  id INTEGER PRIMARY KEY,
  label TEXT NOT NULL,
  qty INTEGER DEFAULT 0
);
INSERT INTO demo (id, label, qty) VALUES
  (1, 'alpha', 2),
  (2, 'beta', 5);
SELECT label, qty FROM demo WHERE qty >= 2 ORDER BY qty DESC;

Comments: create two demo rows, then SELECT qty >= 2 ordered. Say which labels come back.

Short notes

Def-- and /* */ comments. # in MySQL.
RuleSpace after -- .
TrapPassword in a commented dump line.

Comments

Comments — sample query

Short notes

Questions

Comments

Comments — sample query

Short notes

Questions